//! Gossip协议节点发现模块
//! 
//! 实现Redis集群的Gossip协议，用于：
//! - 节点自动发现和加入集群
//! - 集群状态信息传播
//! - 故障检测和故障信息传播
//! - 配置变更通知

use crate::cluster::traits::{
    NodeDiscovery, GossipMessage as GossipMessageTrait, GossipStats as GossipStatsTrait
};
use crate::cluster::{ClusterState, ClusterError, ClusterResult};
use async_trait::async_trait;
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::net::SocketAddr;
use std::sync::Arc;
use std::time::{Duration, Instant};

use tokio::sync::{broadcast, RwLock};
// use tokio::time::{interval, sleep}; // 暂时未使用
use tracing::info;
use uuid::Uuid;

/// Gossip消息类型
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum ClusterGossipMessage {
    /// Ping消息 - 心跳和状态同步
    Ping {
        sender_id: String,
        sender_addr: SocketAddr,
        cluster_state: ClusterStateDigest,
        timestamp: u64,
        sequence_number: u64,
    },
    
    /// Pong消息 - 对Ping的响应
    Pong {
        sender_id: String,
        sender_addr: SocketAddr,
        cluster_state: ClusterStateDigest,
        timestamp: u64,
        ping_timestamp: u64,
        sequence_number: u64,
    },
    
    /// Meet消息 - 请求加入集群
    Meet {
        node_id: String,
        node_addr: SocketAddr,
        cluster_id: Option<String>,
        timestamp: u64,
        sequence_number: u64,
    },
    
    /// Fail消息 - 故障通知
    Fail {
        failed_node_id: String,
        reporter_id: String,
        timestamp: u64,
        reason: String,
        sequence_number: u64,
    },
    
    /// Leave消息 - 节点主动离开集群
    Leave {
        node_id: String,
        timestamp: u64,
        reason: String,
        sequence_number: u64,
    },
}

impl GossipMessageTrait for ClusterGossipMessage {
    fn sender_id(&self) -> &str {
        match self {
            Self::Ping { sender_id, .. } => sender_id,
            Self::Pong { sender_id, .. } => sender_id,
            Self::Meet { node_id, .. } => node_id,
            Self::Fail { reporter_id, .. } => reporter_id,
            Self::Leave { node_id, .. } => node_id,
        }
    }
    
    fn message_type(&self) -> &str {
        match self {
            Self::Ping { .. } => "ping",
            Self::Pong { .. } => "pong",
            Self::Meet { .. } => "meet",
            Self::Fail { .. } => "fail",
            Self::Leave { .. } => "leave",
        }
    }
    
    fn sequence_number(&self) -> u64 {
        match self {
            Self::Ping { sequence_number, .. } |
            Self::Pong { sequence_number, .. } |
            Self::Meet { sequence_number, .. } |
            Self::Fail { sequence_number, .. } |
            Self::Leave { sequence_number, .. } => *sequence_number,
        }
    }
    
    fn timestamp(&self) -> Instant {
        let timestamp_secs = match self {
            Self::Ping { timestamp, .. } |
            Self::Pong { timestamp, .. } |
            Self::Meet { timestamp, .. } |
            Self::Fail { timestamp, .. } |
            Self::Leave { timestamp, .. } => *timestamp,
        };
        
        // 将UNIX时间戳转换为Instant（简化处理）
        Instant::now() - Duration::from_secs(timestamp_secs % 3600)
    }
    
    fn validate(&self) -> bool {
        // 基本验证：检查必要字段是否为空
        match self {
            Self::Ping { sender_id, .. } |
            Self::Pong { sender_id, .. } => !sender_id.is_empty(),
            Self::Meet { node_id, .. } |
            Self::Leave { node_id, .. } => !node_id.is_empty(),
            Self::Fail { failed_node_id, reporter_id, .. } => {
                !failed_node_id.is_empty() && !reporter_id.is_empty()
            }
        }
    }
}

/// 集群状态摘要 (用于快速比较状态差异)
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ClusterStateDigest {
    /// 集群ID
    pub cluster_id: String,
    /// 配置纪元
    pub config_epoch: u64,
    /// 节点数量
    pub node_count: usize,
    /// 在线节点数量
    pub online_nodes: usize,
    /// 分配的槽位数量
    pub assigned_slots: usize,
    /// 状态哈希值 (用于快速检测差异)
    pub state_hash: u64,
}

/// Gossip统计信息
#[derive(Debug, Clone, Default)]
pub struct ClusterGossipStats {
    pub messages_sent: u64,
    pub messages_received: u64,
    pub ping_sent: u64,
    pub pong_sent: u64,
    pub meet_sent: u64,
    pub fail_sent: u64,
    pub update_sent: u64,
    pub errors: u64,
    pub nodes_discovered: usize,
    pub seeds_configured: usize,
    pub gossip_rounds: u64,
    pub last_gossip_time: Option<Instant>,
}

impl From<ClusterGossipStats> for GossipStatsTrait {
    fn from(stats: ClusterGossipStats) -> Self {
        GossipStatsTrait {
            messages_sent: stats.messages_sent,
            messages_received: stats.messages_received,
            nodes_discovered: stats.nodes_discovered,
            seeds_configured: stats.seeds_configured,
            gossip_rounds: stats.gossip_rounds,
            last_gossip_time: stats.last_gossip_time,
        }
    }
}

/// 节点信息
#[derive(Debug, Clone)]
pub struct NodeInfo {
    pub id: String,
    pub addr: SocketAddr,
    pub last_seen: Instant,
    pub last_ping: Instant,
    pub last_pong: Instant,
    pub fail_count: u32,
    pub rtt: Option<Duration>,
    pub is_seed: bool,
}

/// Gossip配置
#[derive(Debug, Clone)]
pub struct GossipConfig {
    /// Gossip间隔
    pub gossip_interval: Duration,
    /// 每次Gossip的目标节点数量
    pub fanout: usize,
    /// 故障检测超时
    pub fail_timeout: Duration,
    /// 最大重试次数
    pub max_retries: u32,
    /// UDP缓冲区大小
    pub udp_buffer_size: usize,
    /// 是否启用UDP广播
    pub enable_udp_broadcast: bool,
}

impl Default for GossipConfig {
    fn default() -> Self {
        Self {
            gossip_interval: Duration::from_millis(100),
            fanout: 3,
            fail_timeout: Duration::from_secs(5),
            max_retries: 3,
            udp_buffer_size: 65536,
            enable_udp_broadcast: true,
        }
    }
}

/// Gossip协议实现
pub struct GossipProtocol {
    /// 本地节点信息
    local_node_id: String,
    
    /// 已知节点列表
    known_nodes: Arc<RwLock<HashMap<String, NodeInfo>>>,
    
    /// 广播通道
    broadcast_sender: broadcast::Sender<ClusterGossipMessage>,
    
    /// 运行状态
    is_running: Arc<RwLock<bool>>,
    
    /// 统计信息
    stats: Arc<RwLock<ClusterGossipStats>>,
}

impl GossipProtocol {
    /// 创建新的Gossip协议实例
    pub async fn new(
        local_node_id: String,
        _local_addr: SocketAddr,
        _cluster_state: Arc<RwLock<ClusterState>>,
        _config: GossipConfig,
    ) -> ClusterResult<Self> {
        let (broadcast_sender, _) = broadcast::channel(1000);
        
        Ok(Self {
            local_node_id,
            known_nodes: Arc::new(RwLock::new(HashMap::new())),
            broadcast_sender,
            is_running: Arc::new(RwLock::new(false)),
            stats: Arc::new(RwLock::new(ClusterGossipStats::default())),
        })
    }
    

    
    /// 获取Gossip统计信息
    pub async fn get_stats(&self) -> ClusterGossipStats {
        self.stats.read().await.clone()
    }
    
    /// 获取消息广播接收器
    pub fn subscribe(&self) -> broadcast::Receiver<ClusterGossipMessage> {
        self.broadcast_sender.subscribe()
    }
}

#[async_trait]
impl NodeDiscovery for GossipProtocol {
    type GossipMessage = ClusterGossipMessage;
    
    async fn start(&mut self) -> ClusterResult<()> {
        {
            let mut running = self.is_running.write().await;
            if *running {
                return Ok(());
            }
            *running = true;
        }
        
        info!("启动Gossip协议...");
        Ok(())
    }
    
    async fn stop(&mut self) -> ClusterResult<()> {
        let mut running = self.is_running.write().await;
        *running = false;
        info!("Gossip协议已停止");
        Ok(())
    }
    
    async fn send_gossip(&self, target: &str, _message: Self::GossipMessage) -> ClusterResult<()> {
        // 根据目标节点ID查找地址
        let addr = {
            let nodes = self.known_nodes.read().await;
            nodes.get(target)
                .map(|node| node.addr)
                .ok_or_else(|| ClusterError::NodeNotFound(target.to_string()))?
        };
        
        // TODO: 实现实际的消息发送
        info!("发送Gossip消息到: {} ({})", target, addr);
        Ok(())
    }
    
    async fn handle_gossip(&mut self, message: Self::GossipMessage) -> ClusterResult<()> {
        // 更新统计信息
        {
            let mut stats = self.stats.write().await;
            stats.messages_received += 1;
        }
        
        // 广播给订阅者
        let _ = self.broadcast_sender.send(message.clone());
        
        info!("处理Gossip消息: {}", message.message_type());
        Ok(())
    }
    
    async fn add_seed_node(&mut self, addr: SocketAddr) -> ClusterResult<()> {
        let node_info = NodeInfo {
            id: format!("seed_{}", Uuid::new_v4()),
            addr,
            last_seen: Instant::now(),
            last_ping: Instant::now(),
            last_pong: Instant::now(),
            fail_count: 0,
            rtt: None,
            is_seed: true,
        };
        
        self.known_nodes.write().await.insert(node_info.id.clone(), node_info);
        
        // 更新统计
        {
            let mut stats = self.stats.write().await;
            stats.seeds_configured += 1;
        }
        
        info!("添加种子节点: {}", addr);
        Ok(())
    }
    
    async fn get_discovered_nodes(&self) -> Vec<SocketAddr> {
        let nodes = self.known_nodes.read().await;
        nodes.values()
            .filter(|node| node.id != self.local_node_id)
            .map(|node| node.addr)
            .collect()
    }
    
    async fn meet_node(&mut self, addr: SocketAddr) -> ClusterResult<()> {
        info!("Meet节点: {}", addr);
        // TODO: 实现实际的meet逻辑
        Ok(())
    }
    
    async fn forget_node(&mut self, node_id: &str) -> ClusterResult<()> {
        if let Some(_) = self.known_nodes.write().await.remove(node_id) {
            info!("忘记节点: {}", node_id);
        }
        Ok(())
    }
    
    async fn get_gossip_stats(&self) -> GossipStatsTrait {
        let stats = self.stats.read().await;
        stats.clone().into()
    }
}

